Current practices in the management of broken bones employ a broad spectrum of mechanical variables. To present, there have been no controlled experimental studies which quantitate the strength of bone as a function of time, and compare the effects of different quantified mechanical variables on rate of fracture healing. During the past year, we have carried out a study in which female New Zealand rabbits were anesthetized and surgical osteotomies were made in the mid-shaft of their tibias. On both tibia, a compressive load of 20 Newtons of force was applied on one of the legs which alternately was left then right. Cyclical loading of an additional 20 Newtons was applied, 55 cycles/minute, 4 hours/day, 7 days/week. At various stages, the animals were sacrificed and a quantitative analysis of bone "strength" was carried out. Four parameters were measured with the use of a torsion testing machine and computer analysis. They were 1) torque to failure, 2) angle at failure, 3) energy absorbed to failure, and 4) stiffness. Results showed a gradual progression of strength in all four parameters with time. It was interesting to find that in these two mechanically different situations, there was no difference in the healing efficiency of the paired tibias in the same animal. The significance of these studies to health care, in general, is close at hand and readily applicable. In this study, cyclical loading, which is more or less equivalent to a walking cast, and rigid compression, which is more or less equivalent to surgical treatment with a plate, showed no difference. Assuming that this trend is confirmed, by subsequent experiments, we must ask ourselves what the advantages are of subjecting a patient to all the risk attendant to elective surgery for the treatment of a fracture that can be treated just as well with a cast.